29 November 2010

The Joule-Doh night light

What do you get if you take a joule-thief and put it inside a play-doh can? A yellow "Joule-Doh" light! (or a "Play-Thief" one?!)

Recently I have re-engineered my homebuilt joule-thief after a too heavy shake that broke one wire. It was a good chance to let my older daughter choose for a new container, and a new color.

An empty play-doh can laying around was chosen as the new night light. The lid holds just right a 1xAA container and a small SPST slide-switch. Wires hold up the LED.

The 5mm while LED gives a quite directional light beam, but the transparentish can allows the light to be diffused around.

The Joule-Doh night light generates enough brightness in a dark 4x5m room so that you can walk around without hitting abandoned toys and tuck your child(ren) up.

For those not familiar with the "Joule thief", it is an oscillating circuit that allows to light a LED out of a 1.5V battery (be it AA, AAA or button). It usually works down to 0.8V, so it is a very good way to drain all the juice from those batteries that won't work anymore in normal toys. This one has been running already for 5 nights off the same "officially discharged" AA battery.

12 November 2010

TTL oscillator as NE602 external source

There are lazy moments in everyone's life when you want to drive the NE602 LO input with a TTL-generated signal. I had asked on the qrp-tech forum few months ago and got helpful replies.

NE602 datasheet reccommends a 200 to 300 mV p-p drive from an external LO.

An application note shows this arrangment with a resistive divider for a TTL signal: 510 and 30 ohm, fed through a 0.1uF capacitor. This results in 277 mVpp for a 0-5V square signal.

Simple, isn't it?

Since I ignore the output switng of the canned oscillator I intend to use, I will try with a 1k multiturn trimmer and tune for an acceptable level.

08 November 2010

FT817 external display, video instructions (it)

Today I think that there is no better way than a video to show a product's features, and to get some feedback about it.

So I produced 5'30" worth of video-instructions for the external frequency readout for transverter users. The audio is in Italian and I will add English subtitles.

Current features were summarized in another post. Please send feedback via email.

05 November 2010

External display for transverter, diagram

Here is the schematic diagram for the external display based on ATmega168 (or mega48 or mega88 or mega328). Click to enlarge:

The component count is as low as possible. You may choose to take the supply from another source than the FT8x7 ACC port, such as a dedicated 9V battery.

You cannot leave out the two N.O. pushbuttons "[Up]" and "[Enter]" ("[Next]" on the diagram), but you can skip the LCD backlight control (mind the total supply current does not exceed 100mA, better less!).

This circuit is also the base for the keypad+display device I am still working on. The keyboard extension chip (PCF8574) will be connected to pins 4-5-6, so leave room for it on your board... in case you'll be interested in that device too.

"Release Candidate 1" ("RC1") firmware is available on request, until I publish it on my website.

Testers needed.

03 November 2010

FT817 external display, revised

The external display firmware for ATmega48/88/168 chips is ready for a public beta.

I have kept a two-button user control interface and changed the LO programming method.

Since the survey (and following emails) showed that it is possible to have 100 Hz accuracy on 47 GHz transverters (WOW!), the display now allows 0.1 kHz resolution both for LO and VFO.
The LO value, 16 values actually, are inserted digit-by-digit through the two buttons when in "config mode".

Updated characteristics are:
  • based on ATmega48/88/168 chip clocked at 11.052 MHz
  • 2*16 character display (HD44780)
  • 2 buttons interaction
  • "config" and "normal" operation modes
  • 16 LO values stored in EEPROM (survive poweroff, can be fewer)
  • LO value down to 100 Hz
  • LO ranges from 0 to 214'748'364'700 Hz (that's 214.7 GHz)
  • VFO/output frequency computed to 100 Hz resolution
  • support for both Out= LO+IF and Out=LO-IF
  • LO value selection by button press (1 > 2 > ... > 15 > 16 > 1 > ...)
  • VFO A/B toggle on second button
The "config mode" is accessed at display powerup by pressing a button. Reboot the display to enter normal operation mode.

I am working on a circuit diagram to be published soon. Who built the ATtiny2313-based display can assemble a simple adapter board for ATmega chips.